The objective is to complete development of a catheter tip device capable of measuring instantaneous flow in the pulmonary artery or the aorta. The principle of operation is based upon ultrasonic detection of blood velocity and vessel cross-sectional area. The product of these gives instantaneous volume flow. We have built and tested the velocity and area components. These work successfully, but require further improvement. We have begun testing catheters with combined velocity and area components, and have obtained reasonable instantaneous flow records and stroke volumes in the pulmonary artery of dogs. We wish to accomplish several specific objectives: (1) develop an automatic processing system so that instantaneous flow, stroke volume, and cardiac output can be generated on line; (2) continue to test the system in dogs for accuracy and safety; (3) make further improvements in catheter and electronics; and (4) test the device in several clinical situations. Our goal is to have a clinically useful device in three years. BIBLIOGRAPHIC REFERENCES: Martin, R.W., Pollack, G.H., and Phillips, J.: An ultrasonic catheter tip instrument for measuring volume blood flow. (IEEE Ultrasonic Symp.) IEEE Trans. Sonics and Ultrasonics, vol. Su, 23, 3, May, 1976. Martin, R.W., Pollack, G.H., and Phillips, J.B.: Stroke volume measurement with an ultrasonic catheter system. Summaries of First World Fed. Ultrasound in Med. & Biol., 111, 1976.